The present invention relates to the production of fatty acid methyl esters from fatty acid triglycerides. In particular, the invention relates to a single-phase process for the transesterification of fatty acid triglycerides with alcohol in the presence of a base catalyst.
The transesterification of vegetable oils to form esters, and in particular, methyl esters, has received considerable attention, primarily because the esters may be used as xe2x80x9cbiofuelsxe2x80x9d or xe2x80x9cbiodieselxe2x80x9d. Biofuels are fuels derived from renewable resources such as naturally occurring fats and oils. Such fats and oils may be obtained from a variety of plant and animals. Biodiesel relates to the specific application to diesel fuel.
The major components of an oil or fat are fatty acid triglycerides, in which three long chain fatty acid moieties are joined to one glycerol moiety by ester linkages, particularly when the fats and oils are in the form of vegetable oils. Other sources of fats and oils contain a significant proportion of fatty acids.
A number of manufacturing facilities have been built in Europe for the manufacture of biofuels, and similar facilities are planned for other countries.
The formation of vegetable oil methyl esters by the base-catalyzed reaction of triglycerides in the vegetable oil with methanol is a two-phase reaction, and is known to be slow. Methanolysis is understood to occur only in the methanol phase. Low oil concentration in methanol causes the slow reaction rate and a slow dissolving rate of the oil in the methanol causes an initiation period. As the concentration increases, the reaction rate also increases. However, the reaction rate subsequently decreases, and the reaction tends to stop before completion.
The problem of the slow reaction rate may be alleviated by the use of non-reactive co-solvents, which result in the conversion of the two-phase system into a single phase. Simple ethers, such as tetrahydrofuran (THF) and methyltertiarybutylether (MTBE), are particularly good co-solvents, as is described in Canadian Patent Application 2,131,654, published Mar. 9, 1996. However, the one-phase process using co-solvents still exhibits a dramatic slowing of the reaction rate. For example, in embodiments of the reaction, about 68% of the ester may be formed in the first minute, but only a total of 77% by the end of the second minute of the reaction. Molar ratios of alcohol to triglyceride of at least 4.5:1 and more preferably at least about 6:1 are disclosed, with typical ratios being in the range of 6:1 to 8:1.
The reaction is discussed by D. G. B. Boocock et al in Biomass and Bioenergy Vol. 11, No. 1 pp 43-50 (1996). Explanations for the slowing of the methanolysis reaction are stated to include possible formation of cyclic products, fall in polarity of the reaction mixture due to methanol depletion or mixing of oil, methanol and cosolvent and depletion of hydroxide ion if present.
U.S. Pat. No. 5,525,126 of Basu et al discloses esterification of mixtures of fats and oils using a calcium acetate/barium acetate catalyst. However, the method requires elevated temperature, in excess of 200xc2x0 C., and elevated pressures of approximately 500 psi. Reaction times are long, being three hours. These conditions render the esterification process impractical and uneconomical for an industrial process.
U.S. Pat. No. 5,713,965 of Foglia et al. discloses use of lipases in the transesterification of triglyceride-containing substances and free fatty acids. Reaction times of 4-16 hours are required in order to obtain conversion rates of 95%, which is not practical for an industrial process.
WO 00/05327 of Ginosar et al. describes use of a xe2x80x9ccritical fluidxe2x80x9d, high temperature and pressure to effect a transesterification reaction.
Improvements in processes for the production of fatty acid methyl esters from triglycerides are required. In particular, a process for the conversion of triglycerides to the corresponding ester in a manner that is fast, essentially complete and is cost effective for both capital and operating costs is required. Such a process would offer potential as an industrial process.
The present application is directed to esterification of triglycerides in the absence of fatty acids.
Processes for the production of fatty acid methyl esters from triglycerides have now been found.
Accordingly, one aspect of the present invention provides a process for the esterification of a triglyceride, comprising:
(a) forming a single phase solution of said triglyceride, an alcohol, a base catalyst for the esterification reaction and a cosolvent at a temperature that is less than the boiling point of the solution, said alcohol being selected from the group consisting of methanol and ethanol, and mixtures thereof, and the ratio of alcohol to triglyceride being in the range of 15:1 to 35:1, the cosolvent being in an amount to effect formation of the single phase; and
(b) after a period of time, recovering ester from said solution.
In preferred embodiments of the invention, the triglyceride is selected from the group consisting of beef tallow, coconut oil, corn oil, cottonseed oil, lard, olive oil, palm oil, palm kernel oil, peanut oil, soybean oil, linseed oil, tung oil, sunflower oil, safflower oil, canola oil, rapeseed oil, sesame oil, babassu oil, perilla oil, oiticica oil, fish oils, menhaden oil, castor oil, Chinese tallow tree oil, Physic nut oil, Cuphea seed oil, microalgal oils, bacterial oils and fungal oils. Preferably, the triglyceride is soybean oil, palm oil, palm kernel oil, coconut oil or canola oil.
In a further embodiment of the invention, the cosolvent is selected from the group consisting of tetrahydrofuran, 1,4-dioxane, diethyl ether, methyltertiarybutylether and diisopropyl ether.
In another embodiment of the invention, the process is a continuous process.